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ZZ4 350 - no horsepower

 
2manyproblems
I love my Chevy Chevette!
Posts: 2
Joined: 09/08
Posted: 09/04/08 11:03 AM

I recent purchased and installed a GM Performance ZZ4 350 in my 68 Camaro.  It was a turnkey package from a GMPP dealer.  It has a GMPP dual plane aluminum intake and a Holley 750 which were installed by the dealer.  The car has a close ratio 4sp followed by a 10 bolt posi and 373 gears.  The timing and carb seem to be setup correctly, the car runs smooth and there are not any unusual noises.  When you get it on the road, it has little to no pull.  How bad is it - it won't even break the tires loose.  I attached a vacuum gauge to the manifold and in the garage the vac is great.  Under hard acceleration, the vac. goes to zero and stays there until you let off the gas.  Under regular acc. it has some pull, but not anything like it should for a 355hp/400ft.lb engine.  I have also been through the carb and made sure the HEI dist has a constant 12V.  What am I missing?  

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Pontiacman2
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Posts: 891
Joined: 01/08
Posted: 09/04/08 12:00 PM

A buddy of mine installed the same crate engine in a costomers 1970 camaro and had to change a lot of parts like the intake,cam+lifters,heads to get it to have some good power. The 355hp. crate engine has no were near what they say it has.  
Pontiacman2
Pontiacman2

Professional Hi-performance engine builder

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55Guy
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Posts: 1153
Joined: 07/06
Posted: 09/04/08 12:15 PM

Something's up, because under acceleration you should still have some vacuum.

Before really tinkering with anything, I'd see about taking it to a shop with a chassis dyno and getting the car run, see how much power it has at the rear wheels. Look at the power bands and start diagnosing what could be wrong from there.  

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JW454
V-6 Camaros rule!
Posts: 81
Joined: 08/08
Posted: 09/05/08 07:20 AM

I fully agree that the horsepower ratings are out to lunch. You should still have decent acceleration though. Holley 750 carb is too big for an engine that is 350cid. and making peak power at 5300rpm. Makes for very lazy low to mid rpm mixture velocities. Good reason for having low or no vaccum when the throttle is stabbed. If you can, borrow a 600cfm carb from someone and give it a try. Always carb as small as possible, without running lean in the top end. Also, what is your base ign. timing set at?  JW.  

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55Guy
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Posted: 09/05/08 01:15 PM

Yep, gotta agree with that, the carb is probably too big for that displacement and the ZZ4 cam. A 600-650 cfm carb will probably do wonders. I'd also find hte specs on your intake, and tlak ot osmeone like Edelbrock or Holley, the intake could be too big for the motor also.  

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DJSOUTH
I love my Chevy Chevette!
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Joined: 09/08
Posted: 09/05/08 01:24 PM

i just go a 1991 camaro rs Laugh  it has the 5.0 v8 but it has the power to go to point a to point b just like that  

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jfh
I love my Chevy Chevette!
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Posted: 09/20/08 08:52 AM

A buddy of mine has the same as the 1 one you have, he put a comp. cams solid roller I think it was 294 duration extrem energy. he runs 7.5 to 7.6 in the 1/8 he has a 750 on that also. they are right I'd check to see why you are loosing vaccum first.  

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cathleen
My first time was in a Chevy
Posts: 161
Joined: 11/08
Posted: 12/15/08 10:58 PM

Ya, start with a little bigger and better hydralic roller cam. think about porting the aluminum heads, you will want to run atleast 92octane when you want to stand on it octane booster is also a noticable help at 10.1 compression specialy with the garbage gas that alot stations   sell.         Also a edelbrock airgap rpm dual plane intake, if you don't have a good set of headers and atleast 2.5" dual flowmasters or something to get that 400ftlbs of tq. you want to get the most possible timming that you can, 3-6deg can be big differences. That motor should run strong and easily spin the tires, the 3.73's might be to tall aswell if it seams like tall gearing that's suited for freeway driving that will be another reason there is no power and you will need to raise the 373's.  It's also possible that cam lobe or two has gone flat and that will also kill performance.

They usually dyno these motor's with the correct header diameter and a good dual exhaust. The numbers are usually right people that dyno generaly know how to tune/setup there motor though.
There's two header diameter's 1 5/8ths and 1 3/4" THE 350's like. 1 5/8ths i think, It can be a difference of 30hp with the wrong diameter. Your probably down 60hp or so, specialy if you have a stock exhaust and tall gearing. you might want 411's  

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.Robin.
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Posted: 12/16/08 07:09 AM

Hi guys,

I am Robin Lawrence. I work with GM Performance Parts on some testing and development. This year I have had 7 different GMPP Crate engines on the dyno. In all cases the engines exceeded the advertised horsepower. On engine was close but 5 horsepower above. All the others were well above the advertised numbers.

I am curious to know several things about your combination. I have not played with the ZZ4 yet so I looked at the specs.  You should be able to turn the tires with that deal.

I wanted to also point out that under WOT you will most likely not see any vacuum. Most of the time if your carb is sized correctly you will see less than 1 inch of vacuum.  It's when the intake and carb are a restriction you will see more than 3 inches of vacuum.

What type of trans?
What stall is the torque converter?
What is the rear end gear?  
How was the timing set?
Did the dealer use the ported vacuum or the manifold vacuum for the distributor hook-up?
Did they set the timing with the vacuum advance disconnected?

Please let me know, I hate when my expectations are not met when I buy some thing.

Robin  

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cathleen
My first time was in a Chevy
Posts: 161
Joined: 11/08
Posted: 12/16/08 10:54 PM

It has a 4speed 373's and a zz350 it should do 11.5sec and burn rubber up the block!  

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mightyman
I love my Chevy Chevette!
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Posted: 12/17/08 05:16 PM

What you missing...  A BIG BLOCK!!!!!!  

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cathleen
My first time was in a Chevy
Posts: 161
Joined: 11/08
Posted: 12/17/08 06:06 PM

ok 12sec  

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cathleen
My first time was in a Chevy
Posts: 161
Joined: 11/08
Posted: 12/18/08 03:08 AM

berrygrant demon 750 A edelbrock AirGap rpm. And a bigger cam or go solid roller and gain another 20-30hp. A holley 750 doublepump works two. The gm carb,intake and  small cam makes for a dull motor. The right headers and exhaust is a absolute must or forget about those advertised numbers  

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.Robin.
I love my Chevy Chevette!
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Posted: 12/18/08 11:58 AM

Dull is a relative term! LOL THe ZZ4 is rated at 350 Horsepower and 418 torque. As mentioned above that should smoke the tires in just about any application.Anyone can take and improve upon a given combination.

It's monday morning coaching. I have played with upgrades on amny of the crate engine and picked up power. These engines are a value for what they represent. If you want to spend more money then there are many options available.

Back to the problem, most of the time I have seen problems it's becasue the timing was not set properly. The OP has not responded to those questions.

If they wanted a big block they should have bought one.

Robin  

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cathleen
My first time was in a Chevy
Posts: 161
Joined: 11/08
Posted: 12/21/08 03:07 AM

they just did another artical on this motor they picked up 117hp with trickflow heads  cam a 750d.p. and also a weiand stealth intake Ibelieve it's looks similar to airgap may be a different name but it was a weiand. Not bad for a mild 10.1 comp 350! Right on par with the mild 383's making 450hp and 480ftlbs average  

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